Submarine signaling



Oct. 21, 1930. J. J. GILBERT 1,778,759

SUBMAR INE S I GNALI NG Filed April 15, 1929 PASS! W /0 7 MM 0006 AL.fiwszrmv- Fruit.)

PASSE 23 /000- /Nl/EN 70/? J J GILBERT A TTOPNEY Patented Oct. 21, 1930UNITED STATES PATENT. oar-"10E JOHN J. GILBERT, or DOUGLASTON, NEW YORK,AssmNoa 'ro BELL TELEPHbNE LABO- aaronms, INCORPORATED, or NEW YORK, N.Y., a CORPORATION or NEW YORK SUBMABINE SIGNALING Application filedApril 15,

The present invention relates to submarine signaling and articularly tothe transmission of voice requency currents over long loaded submarinesignaling cables.

An object of the invention is to increase the number ofsignaling pathsof a submarine signaling cable and thereby to increase the transmissioncapacity of such a cable.

"A further object of the invention is to decrease the maximum frequencyrequired for transmission of speech messages over a long signalingcable.

Another object of the invention is to reduce the cost of submarinesignaling cables.

The attenuation of a long deep sea cable is vastly greater in the rangeof 1,000 to 2,000 cycles than in the range 0 to 1000 cycles and in viewof this fact it is an object of this invention to transmit telephoneconversations over a single cable without employing the frequency rangeabove about 1000 cycles. In a signaling system where two insulatedconductors are available, a ground return circuit may be-employed forthe purpose of obtaining a separate signaling circuit. In the case of anordinary submarine cable having two insulated conductors and an externalconductor consisting of the armor wires and the sea water, two circuitsmay be built up, one comprising the two insulated conductors in series.and the other the two insulated conductors in parallel. having as areturn circuit the armor wires. If the cable has an attenuationsulficiently small and the electrical characteristics of the insulatedconductors are suitably balanced, the circuits which are obtained inthis manner are nearly independent ofeach other. In the case ofa longdeep sea signaling cable, however, the attenuation is very considerableand the level of received speech in the portion of cable ad acent to theterminal of one circuit may fall below the.

level of crosstalk and in order to prevent interference between the twocircuits it would be necessary to provide means so that the speechcurrents would not flow in opposite directions in the various circuitsat any time; If, in this case, the various circuits were used forindependent messages it would be necessary to reverse the direction ofconver- 1929. Serial No. 855,004.

sation of all circuits simultaneously, which arrangement wouldundoubtedly be impracticable from a commercial standpoint.

In accordance with the present invention instead of using the variouscircuits for independent messages they are used for parts of the samemessage. This is accomplished by splitting up the speech frequency bandand shifted back to their original positions before being combined. Inthis manner the maximum frequency that it is required to transmit in anycircuit is very much less than in the case where the cable transmitsspeech of the same quality in the ordinary way and smaller and cheaperconductors may therefore be employed.

In the accompanying drawing which illustrates one embodiment of thisinvention the land line 10 conveys messages having frequencies rangingfrom say 0 to 2000 cycles per second over hybrid coil 11 to filters 12and 13. The hybrid coil 11 is also connected to an artificial line ALfor balancing the land line 10. Filter 12 passes all frequencies between0 and 1,000 cycles per second and filter 13 passes all frequencies above1,000 cycles per second. Modulator 14 modulates the frequencies above1,000 cycles per second. Modulator 14 modulates the frequencies passedby filter 13 with a frequency of 1,000 cycles per second and therebyproduces a frequency band extending from 0 to 1,000 cycles per second,so that the two bands to be transmitted are practically identical inrange. Let us assume speech waves are being transmitted from the landline 10 to the cable 17. Voice-operated relay 15 is operated by thespeech and actuates the armatures of relay 15 to close-the four sets ofcontacts shown at 16 so that the modulated output of device 14 passes tothe two conductors of cable 17 and the unmodulated output of filter 12passes to transformer 18.= When the speech ceases the armatures of relayfall back to their original. positions. Transformer 18 has one terminalof its secondary winding grounded and the other terminal of thesecondary winding is connected to the midpoint of the secondary windingof phantom repeating coil 19. he armor of cable 17 is grounded as shown.Since the two circuits of the cable, metallic and grounded are verynearly alike as regards transmission, the level of speech in the twocircuits, when the two frequency bands are being transmitted, ispracticall the same at all points along the cable. I a reasonable degreeof balance exists between the two cores, the level of interferencepicked up at any point due to cross-talk will be very much lower thanthe level of speech at the corresponding point in the circuit where theinterference is picked up, so that the two speech bands will notinterfere with each other. One method of producing a balanced two-coretelephone cable in combination with which the methods of the presentinvention are particularly suitable has been disclosed in applicantscopending application Serial No. 349,317, filed March 23, 1929.

A suitable receiving network is shown on the lower half of the drawing.Incoming messages of the aforementioned range of frequency bands arereceived over the metallic and superposed cable circuits and areimpressed upon the phantom repeating coil 19. The metallic circuitconducts the frequencies received over it through the back contacts 16of voice operated relay 15 to 1,000-cycle demodulator 20, and thegrounded or superposed circuit conducts the frequencies received torepeating coil 18 and thence through the lowest two contacts of relay 15to filter 21 which passes frequencies from 0 to 1,000 cycles per second.Demodulator receives and demodulates the frequency band which wasmodulated before transmission and brings it back to its originalposition in the speech spectrum. This band is then passed to filter 22which passes all the frequencies over 1,000 cycles per second. The twobands received are combined in amplifier 23 and impressed on hybrid coil11 to be received in the receiver connected to land line 10. Theamplifier 23 also impresses speech energy on voice operated relay 24which operates to prevent the operation of voice controlled relay 15while a speech is being received from the cable and also short circuitsthe path from the hybrid coil 11 to the input side of filters 12 and 13.

In the case of a four-core submarine cable affording four separatesignaling circuits, the speech spectrum from 0 to 2,000 cycles persecond may be divided into four equal bands and all bands except thelowest may be modulated so as to furnish a transmission band extendingapproximately from 0 cycles per second to 500 cycles per second. Oneband would be transmitted over one pair of wires in series, a secondband over the other pair in series, a third band using the conductors ofone pair in parallel as one side of the circuit and the two conductorsof the other air in parallel for a return, while the fourt band wouldemploy all four conductors in parallel with the ground for a return.

The method of signaling in accordance with this invention is ofconsiderable economic value in the case of a telephone cable of about1,800 nautical miles or more. A twin core cable of this length is ofsuch weight and bulk that any reduction in transmission requirementswill effect considerable saving in cost and make the project morepracticable from the standpoint of laying and maintaining the cable.

WVhat is claimed is:

1. A submarine telephone cable system, comprising physical andsuperimposed transmission paths, means for narrowing the range of thefrequencies to be transmitted, and means for transmitting the variousfrequency bands of a message separately over said transmission paths.

2. A submarine telephone system characterized by the provision of aplurality of sig" naling circuits comprising series and parallelcircuits, said system including means for dividing the voice frequencyband to be transmitted into a plurality of sub-bands and fortransmitting the sub-bands separately over the series and parallelcircuits.

3. System in accordance with claim 2 in which the series circuits areenclosed in one armor.

4. System in accordance with claim 1 in which the superposed signalingcurrents proceed over a twin conductor in parallel and return over thearmor wires and sea water in parallel.

5. In a long submarine signaling system, means for dividing a frequencyband to be transmitted into a plurality of sub-bands, means for shiftingthe relative position of said sub-bands with respect to one another,means for transmitting said bands to the distant station comprisingphysical and superposed circuits upon the same conductors, and means forreceiving said bands and for restoring them to their original frequencyposition.

6. The method of transmitting speech waves over a long multi-core cablein a submarine signaling system having a plurality of circuitscomprising at least one ground return circuit, which includes dividingthe speech spectrum into a plurality of speech frequency sub-bands,shifting the relative position of said bands to a lower position so thatthe various frequency bands fall within substantially the sametransmission range, transmitting the shifted bands over a plurality ofcircuits, receiving the bands and restoring them to their originalfrequency position.

7. The method of reducing the maximum frequency to be transmitted over along multicore submarine telephone cable, which com- Erises dividing thespectrum of the speech to e transmitted into a plurality ofsubstantially equal frequency bands, translating the freuencies of allbut one of the bands so as to o tain a transmission band of a frequencylow as compared to the effective frequenc before modulation, transmittinon se arate circuits of the ea le, shifting them back to theirori 'nalposition at the receiving end, and com duce the original speechfrequency band.

In witness whereof, I hereunto subscribe my name this 13th do of A ril,1929;

J HN GILBERT.

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